What exactly is the point here? Note that we lose access to other services in the controller with this approach. That means we then are looking at potentially classes having both ControllerBase and ControllerInterface-cum-whatever-it-is. That's starting to get ridiculous. :-)

ControllerBase is for "thin, not worth testing" controllers. ContainerAware is acceptable there.

FormBase takes a different tactic because forms are not "thin, not worth testing" code. We do want to bother testing those properly.

OK, looking over the patch itself rather than the discussion, this makes more sense to me. I'm still concerned about ending up with thick controllers that access the container directly but... I guess that's going to be a training question either way.